This pilot study is designed to assess the efficacy of various doses of the minor bile acid ursodeoxycholic acid orally on the liver disease associated with cystic fibrosis in children. Measures of liver enzymes(ALT,AST,GGT)and liver excretory and metabolic function by assessment of oral caffeine clearance and hepatobiliary scintigraphy pre and post-treatment with the drug will be assessed. Measurement of serum and duodenal bile acids will be used to assess absorption and biliary bile acid enrichment for various doses of the drug.